20段有用的Java片段一

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这20各个代码段是我在之前学习Java时，在某个网站看到的，当时直接剪到了有道云笔记中，好久不写Java，最近整理笔记，觉得这些小知识作为Reference还是很方便的，所以搬到自己的博客中，向原作者表示感谢！之后在Reference中会随时记录有用的代码片段，以提高开发效率。

下面是20个非常有用的Java程序片段，希望能对你有用。
本篇记录1-10

1 . 字符串有整型的相互转换

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String a = String.valueOf(2);   //integer to numeric string  int i = Integer.parseInt(a); //numeric string to an int

2 . 向文件末尾添加内容

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BufferedWriter out = null;  
try {      
	out = new BufferedWriter(new FileWriter(”filename”, true)); 
	out.write(”aString”);  
	} catch (IOException e) {      
	// error processing code  
	} finally {      
	if (out != null) {
		out.close();      
	}  
}

3 . 得到当前方法的名字

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String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();

4 . 转字符串到日期

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java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

//或者是：

SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );  
Date date = format.parse( myString );

5 . 使用JDBC链接Oracle

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public class OracleJdbcTest  {      
	String driverClass = "oracle.jdbc.driver.OracleDriver";
	Connection con;
	public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException{          
	Properties props = new Properties();
	props.load(fs);          
	String url = props.getProperty("db.url");          
	String userName = props.getProperty("db.user");          
	String password = props.getProperty("db.password");          
	Class.forName(driverClass);          
	con=DriverManager.getConnection(url, userName, password);      }      
	public void fetch() throws SQLException, IOException{
		PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
		ResultSet rs = ps.executeQuery();          
		while (rs.next()){              
		// do the thing you do         
		 }          
		 rs.close();          
		 ps.close();      
	}      
	public static void main(String[] args) {
		OracleJdbcTest test = new OracleJdbcTest();    
		test.init();          
		test.fetch();      
		}  

}

6 . 把 Java util.Date 转成 sql.Date

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java.util.Date utilDate = new java.util.Date();  
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

7 . 使用NIO进行快速的文件拷贝

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public static void fileCopy( File in, File out )throws IOException{
	FileChannel inChannel = new FileInputStream( in ).getChannel();
	FileChannel outChannel = new FileOutputStream( out ).getChannel();
	try{  	
	     	inChannel.transferTo(0, inChannel.size(), outChannel);
	     // original -- apparently has trouble copying large files on Windows              
	     // magic number for Windows, 64Mb - 32Kb)
	      	int maxCount = (64 * 1024 * 1024) - (32 * 1024);              				long size = inChannel.size();
	      	long position = 0;
	      	while ( position < size ){	
	      		position += inChannel.transferTo( position, maxCount, outChannel );
	      	}          
	 }finally{
	  
	  	if ( inChannel != null ){                 
	  		inChannel.close();
	  	}              
	  	if ( outChannel != null ){                  
	  		outChannel.close();
	  	}
	}
}

8 . 创建图片的缩略图

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private void createThumbnail(String filename, int thumbWidth, int thumbHeight, int quality, String outFilename)  
        throws InterruptedException, FileNotFoundException, IOException  
    {  
        // load image from filename  
        Image image = Toolkit.getDefaultToolkit().getImage(filename);  
        MediaTracker mediaTracker = new MediaTracker(new Container());  
        mediaTracker.addImage(image, 0);  
        mediaTracker.waitForID(0);  
        // use this to test for errors at this point: System.out.println(mediaTracker.isErrorAny());  

        // determine thumbnail size from WIDTH and HEIGHT  
        double thumbRatio = (double)thumbWidth / (double)thumbHeight;  
        int imageWidth = image.getWidth(null);  
        int imageHeight = image.getHeight(null);  
        double imageRatio = (double)imageWidth / (double)imageHeight;  
        if (thumbRatio < imageRatio) {  
            thumbHeight = (int)(thumbWidth / imageRatio);  
        } else {  
            thumbWidth = (int)(thumbHeight * imageRatio);  
        }  

        // draw original image to thumbnail image object and  
        // scale it to the new size on-the-fly  
        BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);  
        Graphics2D graphics2D = thumbImage.createGraphics();  
        graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);  
        graphics2D.drawImage(image, 0, 0, thumbWidth, thumbHeight, null);  

        // save thumbnail image to outFilename  
        BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outFilename));  
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);  
        JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(thumbImage);  
        quality = Math.max(0, Math.min(quality, 100));  
        param.setQuality((float)quality / 100.0f, false);  
        encoder.setJPEGEncodeParam(param);  
        encoder.encode(thumbImage);  
        out.close();  
    }

9 . 创建 JSON 格式的数据

请先阅读这篇文章 了解一些细节，并下面这个JAR 文件：json-rpc-1.0.jar (75 kb)

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import org.json.JSONObject;  
...  
...  
JSONObject json = new JSONObject();  
json.put("city", "Mumbai");  
json.put("country", "India");  
...  
String output = json.toString();  
...

10 . 使用iText JAR生成PDFd

阅读这篇文章 了解更多细节

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import java.io.File;  
import java.io.FileOutputStream;  
import java.io.OutputStream;  
import java.util.Date;  

import com.lowagie.text.Document;  
import com.lowagie.text.Paragraph;  
import com.lowagie.text.pdf.PdfWriter;  

public class GeneratePDF {  

    public static void main(String[] args) {  
        try {  
            OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));  

            Document document = new Document();  
            PdfWriter.getInstance(document, file);  
            document.open();  
            document.add(new Paragraph("Hello Kiran"));  
            document.add(new Paragraph(new Date().toString()));  

            document.close();  
            file.close();  

        } catch (Exception e) {  

            e.printStackTrace();  
        }  
    }  
}
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